The separation of particulate material into various sizes may be achieved by a process known as screening, or grading. Such processes are routinely used in the mining, quarrying, and mineral processing industries. Screen boxes for screening or grading processes typically comprise one or more screen decks containing a perforated screening surface that acts as a sieve, through which material of a certain size can pass. Screen decks are generally planar and may be inclined so that, when material to be separated is deposited onto the deck at a receiving, optionally raised, end, the material moves along the screening surface towards a discharge, optionally, lower, end. The screening surface has apertures through which material of a size defined by the diameter of the aperture may pass, thereby separating out material of a defined size from the original input material. The remaining material, which is too large to pass through the apertures, is discharged from the discharge end of the screen deck to be received by, for example, a hopper, chute or conveyor.
Vibrating screen boxes use a vibrating mechanism to assist in the separation process, as well as in the conveyance of the particulate material from a receiving end to a discharge end. Optionally, if the screen deck is inclined, the effect of gravity assists the movement of the material over the screening surface. The efficiency and nature of the screening process is determined by the angle of the screen deck, as well as the vibratory energy imparted to the screen deck. Furthermore, a number of screen boxes may be used in series in order to provide particular screening characteristics for the screening process.
Vibrating mechanisms are employed to impart vibratory energy to the screen deck(s) of a screen box and are characterized by the form of the vibration and the number of bearings used in the screening apparatus. Vibrating mechanisms may produce vibratory motions that include circular, elliptical, and straight-line reciprocal movement. A screen box typically has two or four bearings by which it is mount to a support frame. A screen box having two bearings will have different screening characteristics than a screen box having four bearings. Therefore, depending on the required screening application a two-bearing screen box and/or four-bearing screen box may be required. However, it can be expensive and inconvenient to provide multiple screening apparatus to cover a range of screening requirements, especially when it is desired to use a number of screen boxes in series.
It would, therefore, be desirable to provide a more flexible screening apparatus to mitigate this problem.